I don't have any good methods. I'm not ambidextrous and even if I was I prefer to use two hands so that wouldn't help anyway. So whenever possible I try to let my computer just automate page turns and whatnot over a 30-50 second interval. If not, I have to reach for my mouse quickly.
Someday we'll have better technology to solve this problem though. Your computer will even be able to detect where your eyes are. At that point we could turn the page just by looking at a page button, or maybe our computers will even figure out when we've finished reading a page. Here are my expectations for porn technology advancements.
1. Eye detection software, as mentioned above
2. Automated onaholes
3. Virtual reality porn
4. Sex robots
5. Uploading your consciousness into computers for an immersive sex experience
6. ???
Beyond 5 is unknown territory. Why? If you ever check out sex toys online you'll quickly realize that not all toys are made the same. In fact there are a lot of holes that aren't meant to imitate a human vagina at all. Just as there are a lot of ways to have sex, there are a lot of different ways to stimulate the body. Someday some kinds of porn will become synonymous with masturbation, and transcend both definitions.